1. Field of the Invention
This invention relates generally to devices for implementing a ground connection between a metallic shield of a service cable and a common ground point. More particularly, the present invention relates to a two-part ground clamp connector which mounts to a buried service cable and includes an attachment point for connection of a flexible conductor to establish continuity with a common ground point.
2. Description of the Related Art
A number of devices have been employed for connecting a ground wire with the tubular ground shields of service cables. Most conventional devices employ clamp assemblies of various forms. In applications to which the present invention relates, the cables, clamping devices and associated interconnections are ordinarily positioned within a cabinet, housing or other enclosure to provide protection from the ambient environment. The service cables to which the present invention relates are buried service cables that enter the enclosure for the purpose of interconnection and/or grounding at specified intervals. A number of conventional designs are configured to secure the service cable rigidly or semi-rigidly to a ground point within the enclosure. For such designs, damage to the cables can occur when the enclosure is subject to intense environmental changes and the cables are fixedly positioned relative to the housing. For example, it is not uncommon for such enclosures to heave as a result of frost while the service cables are frozen in position in the ground.
To avoid disruptions of the ground connection possibly caused by shifting of the enclosure relative to the buried cables, it has become common to establish a ground connection with a flexible wire between the cable and a common ground point. For example, U.S. Pat. No. 4,895,525 illustrates a two-part cable shield grounding clamp connector including a threaded stud to which such a flexible grounding wire can be attached. This particular cable shield grounding clamp connector utilizes arcuate inner and outer plates with the inner plate provided with teeth to scrape the inner surface of a metallic shield to establish improved electrical contact. The ""525 patent illustrates a tang projecting outwardly for longitudinally indexing the inner part of the illustrated grounding clamp connector relative to the cable jacket, but lacks means for longitudinally aligning the inner and outer connector parts. Further, the teeth provided on the inner part of the ""525 connector may interfere with installation by, for example, catching and crumpling the thin metallic shield.
Another representative example is described in U.S. Pat. No. 4,571,013, which discloses a connector for cable shields in the form of a strip of metal bent into a U-shape with a stud extending through the legs to engage a nut that clamps the legs together. Teeth project inwardly from each of the inner and outer legs for gripping the cable shield and jacket to resist pull out. By forming the connector from a single bent strip of metal and passing the stud through both legs, the ""013 patent illustrates one approach to maintaining alignment between the inner and outer portions of a cable shield connector. The teeth on the inner leg may also catch the shield during installation. Additionally, once compressed by the nut and stud, the connector may prove difficult to remove without damage to the cable shield.
An alternative approach is exemplified by U.S. Pat. Nos. 5,722,840 for a conductor protector and 6,322,378 for a conductor protector for ground clamp, both assigned to the assignee of the present invention. These patents disclose a ground clamp that surrounds a cable and a received conductor protector. The smooth, arcuate conductor protector is inserted beneath the cable jacket to establish conductive relationship with the ground shield and substantially surround the conductors to protect them from crushing when the clamp is secured around the service cable. These ground clamp assemblies have proven appropriate for their intended use and have been commercially successful. However, they can be costly to manufacture and time consuming to install. Further, the exterior portion of the clamp occupies significant space in what are typically confined enclosures.
There is a need in the art for a less complicated and less costly connector for establishing a reliable electrical connection between a common ground point and the metallic shield of a buried service cable. The connector should be easily installed and removed with minimal damage to the metallic shield of the service cable. The connector should also preferably be of compact design.
A cable shield ground connector in accordance with one embodiment of the present invention comprises an inner part defining a longitudinally extending cable-receiving trough. A threaded stud is fixed to an opposite side of the inner part projecting generally perpendicularly and away from the cable-receiving trough. The trough narrows or converges to a point at one end to ease insertion of the inner part between the core conductors of the cable and the conductive shield. Longitudinally opposed to the point is a tang projecting away from the trough in a similar direction to the threaded stud. The trough is substantially smooth on its inner and outer surfaces as well as the edges leading to the point. The arcuate configuration of the trough enhances the rigidity of the inner part.
A connector outer part includes an aperture for receiving the threaded stud and a guide for receiving the tang projecting from the connector inner part. The outer part is primarily in the form of a longitudinally extending channel, e.g., a substantially planar web connecting longitudinally extending fillets that project generally perpendicular to the web. The fillets strengthen the outer part such that it is substantially rigid along its length. A plurality of teeth extend integrally from each fillet at a jacket-gripping end of the outer part opposite the guide. The teeth are sharp and angled toward the guide to provide improved pull out resistance for the connector.
In preparation for assembling the connector to a cable shield, the cable jacket and metallic shield are slit over a short distance to allow insertion of the connector inner part. The point of the conductor-receiving trough is inserted between the conductors (the core) of the service cable and the surrounding metallic shield, which is in turn surrounded by a thick plastic or rubber jacket. Electrical continuity is established between the conductive connector inner part as it contacts the inner surface of the metallic shield.
A cable shield ground connector in accordance with the illustrated embodiment of the present invention is preferably inserted circumferentially opposite the slit. As a result, the connector is engaged with an intact portion of the metallic shield and cable jacket. The connector inner part is inserted into the cable until the stud contacts the end of the cable jacket. The connector outer part is then placed over the outwardly projecting stud and tang with the jacket gripping end teeth against the outside of the cable jacket. Together, the threaded stud and tang ensure longitudinal alignment of the connector inner part and outer parts. A nut engages the threaded stud to compress the connector outer part against the connector inner part. Tightening the nut causes the teeth projecting from the outer part to dig into the jacket of the service cable. The teeth are angled and pointed so that force exerted to pull the connector out of the cable actually causes the teeth to dig into the jacket. The compressed engagement between the outer and inner connector portions ensures that a large area of the metallic shield is in surface to surface contact with the received inner connector part. A flexible ground conductor is preferably affixed to the threaded stud prior to tightening the clamping nut.
An object of the present invention is to provide a new and improved cable shield ground connector that is efficiently installed and removed.
Another object of the present invention is to provide a new and improved cable shield ground connector that exhibits improved pull out resistance.
A further object of the present invention is to provide a new and improved cable shield ground connector of efficient and economic design.
A yet further object of the present invention is to provide a new and improved cable shield ground connector of compact configuration.